FIG. 1 is a block diagram illustrating a UMTS (universal mobile telecommunications system) network structure.
Referring to FIG. 1, the UMTS system includes a terminal (user equipment (UE)), a UMTS terrestrial radio access network (UTRAN) and a core network (CN). The UTRAN includes at least one radio network sub-system (RNS). Each RNS includes one radio network controller (RNC) and at least one base station (e.g., node-B) managed by the RNC. At least one cell exists for each node-B.
FIG. 2 is a diagram illustrating a radio interface protocol architecture between a terminal and a UTRAN. As such, FIG. 2 depicts a radio interface protocol architecture based upon a 3GPP (third generation partnership project) radio access network specification between the terminal and the UTRAN.
Referring to FIG. 2, the radio interface protocol is horizontally arranged to include a physical layer, a data link layer, and a network layer. Furthermore, the radio interface protocol is vertically divided into a user plane for data information transfer and a control plane for signaling transfer. The protocol layers may also be divided into an L1 (first layer), an L2 (second layer) and an L3 (third layer) based upon the lower three layers of an open system interconnection (OSI) model.
The first layer or physical layer provides an upper layer with an information transfer service using a physical channel. The physical layer is connected to an upper layer called a medium access control (MAC) layer through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data is also transferred between different physical layers, i.e. between physical layers of a transmitting side and a receiving side, through the physical channel.
The MAC layer of the second layer provides an upper layer called a radio link control layer with a service through a logical channel. A radio link control (RLC) layer of the second layer supports reliable data transfer and performs segmentation and concatenation of a service data unit (SDU) received from an upper layer.
A radio resource control (RRC) layer at a lower portion of the L3 layer is defined in the control plane and controls logical channels, transport channels, and physical channels for configuration, re-configuration and release of radio bearers (RBs). A RB is a service provided by the second layer for data transfer between the terminal and the UTRAN. The configuration of the RBs includes defining characteristics of protocol layers and channels required to provide a specific service, and configuring respective specific parameters and operation methods.
A multimedia broadcast/multicast service (MBMS) is described below.
An MBMS provides a streaming or background service to a plurality of UEs using a downlink dedicated MBMS bearer service. An MBMS includes at least one session. MBMS data is transmitted to a plurality of the UEs via the MBMS bearer service during an ongoing session.
The UTRAN provides the MBMS bearer service to UE using a radio bearer (RB). A point-to-point radio bearer is a bi-directional radio bearer and includes a logical channel DTCH (dedicated traffic channel), a transport channel DCH (dedicated channel), and a physical channel DPCH (dedicated physical channel) or a physical channel SCCPCH (secondary common control physical channel). A point-to-multipoint radio bearer is a unidirectional downlink. The point-to-multipoint radio bearer includes a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel), and a physical channel SCPCH. The logical channel MTCH is configured for each MBMS offered to a cell and is used to transmit user-plane data related to a specific MBMS to a plurality of UEs.
FIG. 3 is a diagram illustrating an example of channel mapping for reception of a point-to-multipoint service by a terminal.
Referring to FIG. 3, a logical channel MCCH (MBMS control channel) is a point-to-multipoint downlink channel and is used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). At least one MCCH exists within a cell.
The UTRAN that offers the MBMS transmits MCCH information to a plurality of UEs via the MCCH channel. The MCCH information includes a notification message associated with the MBMS (e.g., RRC message associated with the MBMS). For instance, the MCCH information may include a message providing notification of MBMS information, a message providing notification of point-to-multipoint radio bearer information, and/or access information providing notification of an EEC connection being requested for a specific MBMS.
FIG. 4 is a diagram illustrating transmission of control information for the point-to-multipoint service.
Referring to FIG. 4, the MCCH information is periodically transmitted according to a modification period and a repetition period. The MCCH information is divided into critical information and non-critical information. Among the critical information and non-critical information, the non-critical information may be modified at a modification period or a repetition period. However, the modification of the critical information may be made only at a modification period. Therefore, the critical information is repeated once during each repetition period in order to be transmitted. However, the transmission of the modified critical information may only occur at a start point of a modification period.
The UTRAN periodically transmits a physical channel MICH (MBMS notification indicator channel) to indicate whether the MCCH information was updated during the modification period. Therefore, a UE attempting to receive only a certain MBMS does not receive the MCCH or MTCH until a session of the certain MBMS service begins. However, the UE does receive a MICH (MBMS notification indicator channel) periodically. An update of the MCCH information is a generation, addition, modification and/or removal of a specific item of the MCCH information.
Once a session of a specific MBMS begins, the UTRAN transmits an NI (notification indicator). The NI is an indicator that provides notification to receive an MCCH channel to a UE attempting to receive a specific MBMS. Upon receiving the NI via an MICH, the UE receives an MCCH during a specific modification period indicated by the MICH.
A UE attempting to receive a specific MBMS using a point-to-multipoint radio bearer receives MCCH information including radio bearer information via an MCCH and then configures the point-to-multipoint radio bearer using the received information. After configuring the point-to-multipoint radio bearer, the UE continues to receive a physical channel SCCPCH to which an MTCH is mapped, in order to acquire data related to the specific MBMS transmitted via the MTCH.
FIG. 5 is a diagram illustrating transmission of point-to-multipoint service data and scheduling information.
Referring to FIG. 5, a UTRAN may transmit MBMS data discontinuously via an MTCH. In so doing, the UTRAN periodically transmits a scheduling message via an SCCPCH (SCCPCH carrying MTCH), to which an MTCH is mapped, to a UE. In such case, the scheduling message provides a transmission start timing point and a transmission section of MBMS data transmitted during a single scheduling period. To this end, the UTRAN informs the UE of a transmission period (scheduling period) of scheduling information.
The UE acquires the scheduling period from the UTRAN and receives the scheduling message periodically according to the acquired scheduling period. The UE then receives the SCCPCH (SCCPCH carrying MTCH), to which the MTCH is mapped, discontinuously and periodically using the received scheduling message. Thus, using the scheduling message, the UE receives the SCCPCH carrying the MTCH during a timing section for which the data is transmitted but does not receive the SCCPCH carrying the MTCH during a timing section for which the data is not transmitted.
However, in the conventional method, the UE continues to receive the scheduling messages periodically even if there is no data transmission for several scheduling periods. Therefore, UE resources, such as a battery power, may be wasted. Furthermore, the UE checks the scheduling messages periodically regardless of a presence or non-presence of the data transmission. In a case where no data is transmitted, the UE may not need to receive the SCCPCH carrying the MTCH. However, in such a case, the UE still needs to periodically check the scheduling messages. Therefore, the UE may consume UE resources to receive the SCCPCH carrying the MTCH.